$headerPrefix = Yii::app()->params['email.custom.header.prefix'];
$emailParams['headers'] = array(
array('name' => $headerPrefix . 'Campaign-Uid', 'value' => $campaign->campaign_uid),
array('name' => $headerPrefix . 'Subscriber-Uid', 'value' => $subscriber->subscriber_uid),
array('name' => $headerPrefix . 'Customer-Uid', 'value' => $customer->customer_uid),
array('name' => $headerPrefix . 'Customer-Gid', 'value' => (string)intval($customer->group_id)), // because of sendgrid
array('name' => $headerPrefix . 'Delivery-Sid', 'value' => (string)intval($server->server_id)), // because of sendgrid
array('name' => $headerPrefix . 'Tracking-Did', 'value' => (string)intval($server->tracking_domain_id)), // because of sendgrid
array('name' => 'List-Unsubscribe', 'value' => $listUnsubscribeHeaderValue),
***** THIS LINE ?? ****array('name' => 'List-Id', 'value' => $list->list_uid . ' <' . $list->display_name . '>'),
array('name' => 'X-Report-Abuse', 'value' => 'Please report abuse for this campaign here: ' . $reportAbuseUrl),
array('name' => 'Feedback-ID', 'value' => $this->getFeedbackIdHeaderValue($campaign, $subscriber, $list, $customer)),
// https://support.google.com/a/answer/81126?hl=en#unsub
array('name' => 'Precedence', 'value' => 'bulk'),